The invention relates to a gear motor in which a pressure plate is arranged at at least one side of gear wheels and is pressed into engagement therewith by fluid pressure in two concentric preliminary outer and main inner pressure areas with a control valve controlling pressure in the radially inner main pressure area. In such known gear motor, there is the disadvantage that the pressure medium control between the preliminary pressure area and the main pressure area does not function satisfactorily, so that the pressure build up in the main pressure field is not effected in a perfect manner.